Velocity modulation apparatus



April 5, 1949. R. WATHEN ET AL VELOCITY MODULATION APPARATUS Filed June 28, 1943 FIG. 3

FIG. 2.

11 FIG. 5.

INVENTORS 625$: BY lAN p flm TTORNEY Patented Apr. 5, 1949 UNITED STATES PATENT OFFICE '2;466,064 vELoorrY MODULATION APPARATUS Robert L. 'Wathen, :Hempstead, and Russell H.

Varian, Garden City, N. Y.,-assignors to The I Sperry Corporation, a corporation of Delaware Application June28, 1943, Serial No. 492,498

'16Claims. 1

This invention relates to grouped electron beam apparatus and is more "particularly concerned with arrangements for improving the e'ificienc'yof the same.

As its preferred embodiment the invention will be described as concerned with apparatus oi the type disclosed in United States Letters Patent No. 2,242,275 and No. 2,259,690, for example, wherein an electron beam having electrons at least partially segregated into longitudinally spaced concentrations travels along a drift or like passage prior to interaction with an electromagnetic fie'ld oscillating at frequencies of "3x10 to 3 I0 cycles .per second and higher.

In such devices, space charge efiect due 'to mutual repulsion of the negatively charged electrons in the electron concentrations usually :cause radial dispersion of those electrons, and some 'of the dispersed electrons are collected by the positively charged passage walls before interaction with the electromagnetic field, resulting in considerable loss of energy from the beam. The present invention reduces such loss and uses the space charge efiects to otherwise improve the efiiciency of operation of such'devices.

It is therefore a major object of the'invention to provide structurally novel apparatus of the grouped electron beam type having improved efficiency.

A further object of the invention is to "provide grouped electron beam apparatus having novel electrode construction for improved operating eificien'cy.

It is a further object of the invention to provide a novel grouped electron beam device wherein an electron beam having the electrons thereof at least partly segregated into longitudinally spaced concentrations is passed in energy exchanging relation with an alternating electromagnetic field, and embodying arrangements for obtaining optimum relation between the energy given up to the field by the electron concentrations of the beam and energy taken from theheld by the electrons in the beam between said*concentrations. Preferably the electrons in the beam between the concentrationsare almost entirely intercepted so that the field does no Work on the beam. The device may be employed-as anamplifier, detector or the like.

A further object of the invention is to provide a novel grouped electron beam device'wherein an electron grouped beam is passed through' a hollow resonator, and arran'gernents arejpr'ovided for intercepting electrons in the beam between 4 the electron groups, for producinghigh effective driving currents through the resonator.

A further object of the invention is to provide cavity resonator type apparatus having novel-arrangements for intercepting a portion of an electrongrouped beam for preventing interaction of said portion with an electromagnetic field in the apparatus. It is a further object of the invention to'provide an electron dischargedevice wherein an electron beam having electrons arranged in longituldinally'spaced concentrations is passed in energy interchanging relation with an electromagnetic field and special arrangements "are provided for intercepting electrons in the beam between the concentrations.

"A further object of the invention is to provide a hollow resonator device embodying novel electrode cooling arrangements.

A further ob'ject'of the invention is to' provide novel cavity resonator apparatus wherein a substantiallyannular electron beam is subjected to "predetermined focusing action for reducing losses ter of a cavity resonator type amplifier, or "detector illustrating a preferred embodimentof the invention wherein an annular electron beam is projected through the res onator;

, Fig.2'is a section along line 2-2 of Fig. l;

fFig. 3 is a section along line 33 of Fig. 1;

' Fig. 4 is a section through the longitudinal center of a cavity resonator device comprising a further embodimentof the invention having different electrode arrangements at the output resonator; and

'Fig. 5 is a section along line 5-5 of Fig. 4. Referring now to Fig. 1, a hollow cylindrical body it surrounds a concentric cylindrical drift tube 12 secured thereto by an annularwalliii which divides the interior of the body into resonator chambers I0 and 20. The opposite ends of "the" drift tube and the adjacent end walls of resonat'or casing II are provided with apertured'gri-d electrodes, input electrodes and -l5'being indicated atone end, and outputelectrodes Hi and I! being indicated at the other'end.

I Output grid lectrode I6 is formed at its c'en- 'ter'with a solid "disc-like plate 18 which is prefrably impervious to passage of electrons, and the I B is of the construction shown in Figure 3, with the grid slats supporting rod 2I being intermediately crimped as at I9, so as to provide freedom for expansion when the device gets hot during operation. Rod 2I is thus suspended between grids I5 and I6 through expansion compensating en-d connections. Grids I4 and I! are preferably of conventional construction.

A glass closure member '23 seals one end of resonator I i and extends about a cathode 24 having an annular electron emission surface 25 concentric with the resonator axis. The cathode is heated indirectly by a filament 26 suitably energized by battery 21.

Cathode 24 is also connected to a suitable source of driving voltage such as battery 28, the positive battery terminal and the resonator walls being grounded to provide a complete electrical circuit.

A concentric cylindrical focusing electrode 29 is suitably mounted within closure 23 to surround the electron beam emitted from the oathode, and electrode 29 is energized from battery 28 through a suitable, adjustable potentiometer connection indicated 'at 3 I.

A concentric conical collector electrode 32 designed to prevent secondary emission electrons from entering the resonator is arranged to receive the electron beam after passage through the resonator. A suitable utilization device 32 is connected to electrode 32 so that the device may be used as a. detector as will appear. Electrode 32, like closure 23, is sealed to the adjacent end wall of the resonator, the interior of the resonator being evacuated. A coaxial line coupling of suitable type indicated at is provided for introducing high frequency energy into resonator chamber I0, and a similar coupling 33 is provided for extracting amplified high frequency energy from resonator chamber 20.

In operation a hollow annular beam of electrons is projected from cathode surface 25 into the resonator I0. While this beam is passing through the gap between electrodes I4 and I5, the electrons in the beam are alternately accelerated and retarded by the oscillating electromagnetic field within resonator chamber I0 so as to produce recurrent electron concentrations after its subsequent passage along the drift passage. The electron grouped beam passes through the gap between electrodes I6 and I! in such phase with the alternating field in resonator chamber 20 that energy is extracted from the beam by interaction between the field and the electron concentrations along the beam. The above operation of such a device is known and described in said Patents Nos. 2,242,275 and 2,259,690, and needs no further explanation.

It will be understood, at this point, that the invention is independent of the particular manner of obtaining electron concentrations along the beam, so that any suitable manner of producing such electron concentrations may be employed instead of the input electrode and associated field arrangements at I4, I5. For example, such concentrations may be produced by space charge con- 4 trol in a known manner, as in Haefi' Patent No. 2,237,878.

As the electron concentrations in the beam pass along the drift tube, space charge effects due to mutual repulsion of the electrons in the concentrations cause radial dispersion of the electrons in those concentrations. These space charge effects are not sudden but assert themselves substantially concomitantly with the electron concentration, and their action is not regarded as serious until dispersion becomes sufficient to produce loss of electrons to the drift passage walls. In order to prevent these radially dispersed electrons from being prematurely lost to the drift tube walls, focusing electrode 29 is sufficiently energized to provide a convergent hollow beam of electrons in the resonator at least partly focused on plate I8 as indicated. Where the device is used as a detector, the beam is focused as sharply as possible on plate I8. Where the device is used as an amplifier, the beam is only partly focused on plate I8, to obtain optimum operation resulting from the effect of the changing input signal on the beam focus.

For the sake of illustration, a point 34 is indicated in Fig. 1 to designate a region wherein space charge efiects cause appreciable radial dispersion of the electrons, and the outer envelope of the increasing dispersion is approximately indicated by diverging dot-dash lines in Fig. 1. The actual envelope of such dispersion is probably a smoothly varying curve originating near grid I5, but the above is deemed sufi'lcient for full understanding of the principles of the invention. 1

By the time electron concentrations reach the output electrode gap in proper phase for giving up energy to the associated field, this radial dispersion from the focused beam is only such that the electron beam at the concentrations has relatively small cross-sectional diameter, and undesired loss of electrons from the groups to the drift tube walls is prevented.

Where the device is used as a detector, the beam should be entirely focused on plate I8, with no signal introduced on line 30. Under such conditions, the dispersed annular electron concentrations may pass through an annular grid having only ab out twice the focal diameter. In the drawings the dispersion is shown somewhat exaggerated for purposes of illustration of the principle involved. In any event, of course, the, expanded beam diameter should be less than that of the drift tube.

The above arrangement insures that the appearance of a signal online 30 causes an increase in current fiow through the resonator, which in-' crease is noted at the utilization device 32'.

The annular beam form insures that, when the beam has its maximum enlargement due to space charge, most of the electrons in the concentrations will pass through the annular output grid opening, and when the'beam reaches its minimum diameter, between the electron concentrations, practically none of the electrons will pass through the grid opening.

The electrons in the beam between the electron concentrations, having no appreciable space charge effects, are, as stated above, accurately focused on plate I8 by the action of electrode 29, so that almost all of these electrons are collected by plate I8 and rod M. This means that when the alternating field between grids I6 and I1 is in the direction of movement of the beam there is no interaction between the beam and field. Plate I8 and rod 2| thus prevent interaction between the beam and field during periods between the electron concentrations and when the beam would tend to extract energy from the field, and thus prevent waste and loss in efficiency.

As shown in Fig. 1, rod 2| intercepts many of the electrons in the focused regions between the electron groups in the beam well in front of plate (8. Plate l8 alone would accomplish the electron interception action contemplated by the invention, but probably there would be difficulties due to its high heating from electron bombardment. Rod 2| comprises an effective extension of plate l8 to take the load off plat l8. For this purpose rod 2| need not extend back to button 22 as illustrated, but it preferably does extend to button 22 for support and to assist grid slats I!) in conducting heat away from the grid structure at I6. Preferably also, rod 2| is of about the same diameter as plate I8 as illustrated, so as to provide a large electron interception and heat conducting and radiation surface.

In the above described embodiment of the invention, the use of an annular beam reduces the current which is not expanded into theannular output grid opening during the space charge expanded interval while making sufficient electrons available for efficient interaction with the field. This represents low power consumption for desired output. Efiiciency is appreciably increased by interception of the focused electrons between th concentrations in the beam. This provides that the field extracts optimum energy from the beam, and prevents the beam from regaining any energy from the field. The effective current energizing the output resonator portion is increased, and operation of the device at high power is made possible by adequate cooling of plate 18.

While a small amount of energy is lost due to interception of the thinly distributed electrons at the center of the electron concentrations by plate is, this is more than compensated by the advantage gained by eliminating that portion of the beam normally phased to take energy from the field. In fact, this advantage is such in general that the invention may be employed to advantage in many devices even where the electron beam is solid, instead of annular as illustrated.

Where the device is used as an amplifier, the electron beam is preferably only partly, about half, focused on plate I8 and rod 2|, some of the electrons between the concentrations being permitted to pass through grid l6 and interact with the field. This greatly aids the amplifying action. The invention also may be used as a frequency multiplier, as by designing chamber 20 to resonate at a frequency which is a harmonic of that of chamber I0, or by incorporating it in a device of the kind illustrated and described in .Hansen et al. Patent No. 2,281,935.

While the particular cavity resonator device .ilustrated is an amplifier, such may be employed as an oscillator by interconnecting lines 30 and 33, and it is equally obvious that the invention is applicable to other cavity resonator devices.

As above stated, it is further not necessary to the invention that the original electron grouping of the beam be produced by velocity modulation as indicated in the preferred embodiment, as electron grouping may be produced otherwise as by space charge control, without departing from the spirit of the invention.

Figures 4 and 5 illustrate another form of resonator embodying important phases of the invention. A ihollow cylindrical resonator Tbody35 is internally separated into two resonator chambers 36 and 31 by a wall 38. Wall 38 is centrally apertured to sup-port a concentric drift tube 39 Which is aligned with tubes 4| and 42 projecting inwardly from the opposite end walls of the resonator as illustrated. A beam of substantially uniform cross-section instead of the annular electron beam described in Fig. 1 is projected from cathode 24 through the drift tube.

The adjacent ends of tubes 39 and 4! combine as electrodes to define a continuous aperture 43 surrounding the electron beam and through which the electron beam is coupled to the field of input resonator 36, while the adjacent ends of tubes 39 and 42 combine as electrodes to define a similar continuous aperture 44 through which the electron beam is coupled to the field of output resonator 3'1. Where tubes 39, ll and 42 are cylindrical, apertures t3 and M are circular and this is a preferred form.

Concentric with tube 42 is a smaller diameter concentric reentrant pole 45 having a fiat face .46 disposed perpendicular to the beam and located so as to intercept the center of the beam in advance of aperture 44.

The electron beam projected from cathode 24 is subjected to electron acceleration and retardation forces by the indicated field at aperture 43, thus resulting in recurrent electron concentrations after passing through the tube 39. Similarly to Fig. 1, focusing electrode '29 is energized to focus the electron beam on face 46 and to thereby control radial dispersion of the electrons in the electron concentrations along the beam and prevent loss of electrons to the drift tube walls while utilizing such dispersion to obtain efficient interaction of the beam with the field available at aperture 44. The device may be made somewhat more eflicient, under certain circumstances, by employing the annular electron beam of Fig. l.

The device of Fig. 4 is especially practical and useful in that tube 45 provides ample means for efficiently conducting heat away from face 46, which corresponds to plate I78 in Fig. 1.

The outer electrons of the electron concentrations in the beam, the approximate envelope of which is indicated in diverging dot-dash lines extending from point 34' in Figure 4 similarly to Figure 1, interact with the output field through aperture 44, while the electrons between the concentrations in the beam are focused on and collected by face 46, and are thereby prevented from interaction with the field.

The above arrangement is especially useful with the gridless typeof output resonator shown in Fig. 4 because the outer electrons of the concentrations give up energy to the strongest field regions adjacent aperture 44, the electrons of the concentrations intercepted by face 46 being those electrons which would otherwise interact with relatively weak field portions and thereby contribute but little energy to the field. Whatever unavoidable disadvantage is caused by this latter, it is more than compensated by blocking off those portions of the beam-which might extract energy from the field.

If desired, grid electrodes such as at I4, IS in Fig. 1 may be employed at input resonator 36, or any. other suitable arrangement may be provided for producing electron grouping in the beam. Moreover, the invention of Fig. 4 may be embodied in oscillators, amplifiers and the like as in Fig. l and as illustrated in said Patents 2,242,275 and 2,259,690. While simple resonator .shapes have been shown to illustrate the inven- 7 tion in principle, it can be appliedequally well to resonators shaped as figures of revolution of the shapes of Figs. 1 and 4 about any selected axes, similarly to the devices at Fig. 5 of said Patent No. 2,242,275 and Figs. 7, 12 and 15 of Patent No. 2,259,690 for example.

The present invention is to be distinguished from the invention disclosed and claimed in Serial No. 490,962, filed June 16, 1943. by Russell H. Varian and Morris Relson entitled High frequency apparatus utilizing electron debunching. This application eventuated into Patent No. 2,414,843 granted January 28, 1947. In the latter invention, the electron beam having spaced concentrations in electron density therealong encounters an apertured baflie which eliminates the electrons in the outer annulus of those concentrations. The electron beam passed by the baffle has relatively low electron density at said regions of former concentration, and has relatively high electron density between those regions, so that the passed electron beam is 180 out of phase with the high frequency current which originally produced the electron concentrations.

In the present invention, the electron beam current delivered to the output is in phase with the original high frequency current producing the electron grouping.

As in the above identified Varian and Relson application, the principles of the present invention may be applied to ultra high frequency devices of the type shown in the patent to Hahn No. 2,190,515 and said I-Iaefi patent as well as to the other devices described for illustrative purposes therein, without departing from the spirit of the invention.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Ultra-high-frequency apparatus comprising means for producing an electron stream, a cavity resonator positioned along the path of said stream in velocity-modulating relation thereto, a second cavity resonator positioned along said stream in energy-extracting relation thereto. means defining a field-free drift space between said resonators, whereby said velocity-modulated electrons become grouped electron converging means along said path for focusing said stream to a predetermined point in the vicinity of the second resonator, and electron collecting means located in advance of said point for collecting electrons between the spaced groups of said stream to prevent interaction thereof with said second resonator.

2. Ultra-high-frequency apparatus comprising means for producing an electron stream, means along the path of said stream for velocitymodulating the electrons of said stream, means defining a field-free drift space surrounding the path of said velocity-modulated stream, whereby the electrons of said stream become grouped into spaced concentrations by velocity-grouping action, means beyond said velocity-modulating means for extracting high frequency energy from said grouped stream, electron interceptor means extending concentrically of said drift space between said velocity modulating and energyextracting means for collecting electrons of said stream between said groups to prevent their interaction with said energy-extracting means, and electron focusingmeans along the path of said stream for focusing said stream toward a predetermined point in the vicinity of said energyextracting means, said electron interceptor means being located in advance of said predetermined point.

3. Apparatus as in claim 2 in which said electron focusing electrode means are located coaxial with said means for producing an electron stream and positioned intermediate said means for producing an electron stream and said velocity-modulation means.

4. Ultra-high-frequency apparatus comprising hollow resonator means adapted to maintain an oscillatory electromagnetic field, said means having a gridless aperture, means aligned with said resonator means for producing an electron beam having longitudinally spaced concentrations in electron density therealong and further having electrons of lesser density along the axis of said beam between said concentrations, electronconverging electrode means concentric with said beam producing means for focusing said fewer electrons to a predetermined point, electroncollecting means extending axially and centrally of a portion of said resonator means and having a conductor surface located substantially at right angles to the axis of said beam on one side of said aperture and forwardly of said predetermined point for collecting said fewer electrons prior to their interaction with said field, whereby said concentrations are projected through said field.

5. Ultra-high-frequency apparatus comprising hollow resonator means adapted to contain an oscillatory electromagnetic field, means in said apparatus aligned with said resonator means for providing an electron beam having longitudinally spaced electron concentrations in density therealong and intermediate electrons between said concentrations, said resonator means having an aperture for coupling said field with said beam, electron focusing means along the path of said beam for focusing said beam to a predetermined point in the vicinity of said aperture and for projecting said intermediate electrons to said point, and an electron collector axially aligned with said focusing means and located forwardly of said predetermined point and having a conductive surface laterally of said beam adjacent said aperture.

6. Apparatus as provided in claim 5 in which said electron collector is concentric with and extends axially through a part of said aperture.

7. Ultra-high-frequency apparatus comprising hollow resonator means adapted to maintain an oscillatory electromagnetic field, said resonator means having an aperture, means aligned with said aperture for projecting through said aperture an electron beam having electrons substantially in spaced concentrations in density therealong. further means including an electron collector member having a conductive surface located substantially centrally of said beam, said collector member further being aligned with said aperture in the path of a portion of said beam before said aperture for removing some of the electrons from said beam prior to interaction of said beam and said field, and electron-converging means coaxial with said aperture for focusing said portion of said beam to a point in the vicinity of said aperture.

8. Ultra-high-frequency apparatus comprising hollow resonator means adapted to contain a cyclically varying electromagnetic field, said resonator means having an aperture, means aligned with said aperture for projecting through said aperture an electron beam having electrons substantially in spaced concentrations in density therealong with fewer electrons between said concentrations, said concentrations causing radial dispersion of the beam in their vicinity, electron-focusing means coaxial with said aperture for directing said electrons between said concentrations to a predetermined point in the vicinity of said aperture, and electron collecting means located in the path of said beam before said aperture and having a conductive surface positioned substantially axially of said beam for removing said fewer electrons between said concentrations from said beam prior to interaction of said beam and said electromagnetic field.

9. Ultra-high-frequency apparatus comprising hollow resonator means adapted to contain an oscillatory electromagnetic field, electrode means in front of said resonator means for projecting through said resonator means an electron beam having longitudinally spaced electron concentrations in density therealong, said resonator means being apertured for coupling said beam to said resonator field and including a grid through which said beam is to be projected into said resonator means, and an electron interceptor member substantially concentric with said electrode means for removing electrons from the central zone of said beam prior to interaction between the beam and field, said interceptor member comprising a conductive member secured to said grid and substantially in axial alignment with said beam.

10. Ultra-high-frequency apparatus comprising means for producing an electron stream, a cavity resonator positioned along the path of said stream in velocity-modulating relation thereto, a second cavity resonator positioned along said stream in energy-extracting relation thereto, means defining a field-free drift space between said resonators, whereby said velocity-modulated electrons become grouped and electron collecting means within said drift space for collecting electrons between the spaced groups of said stream to prevent interaction thereof with said second resonator.

11. Ultra-high-frequency apparatus comprising means for producing an electron stream, means along the path of said stream for velocitymodulating the electrons of said stream, means defining a field-free drift space surrounding the path of said velocity-modulated stream, whereby the electrons of said stream become grouped into spaced concentrations by velocity-grouping action, means beyond said velocity-modulating means for extracting high frequency energy from said grouped stream, and electron interceptor means extending axially and concentrically of said drift space between said velocity-modulating and energy-extracting means for collecting electrons of said stream between said groups to prevent their interaction with said energy-extracting means.

12. A cavity resonator device comprising a drift tube of conductive material, grids at opposite ends of said tube, and a conductive member within said tube contiguous with and supported at opposite ends by said grids.

13. The apparatus defined in claim 8, wherein said electron collecting means comprises a conductive member supported in substantial axial alignment with said path.

14. The apparatus defined in claim 16, comprising a support in said apparatus for said electron interceptor means having good heat conducting properties for enabling high power operation of said apparatus.

15. Ultra-high-frequency apparatus comprising hollow resonator means adapted to contain an oscillatory electromagnetic field, electrode means in front of said resonator means for projecting through said resonator means an electron beam having substantially longitudinally spaced electron concentrations in density therealong, electron-converging means concentric with said resonator for focusing said beam at a predetermined point, said resonator means having an aperture for coupling said beam to said resonator field, and an electron-collecting means substantially coaxial with said electrode means and located in the vicinity of said predetermined point and between said projecting means and said aperture for removing electrons from the centralzone of said beam prior to interaction between said beam and field.

16. Ultra-high-frequency apparatus comprising hollow resonator means adapted to contain an oscillatory electromagnetic field and having a substantially continuous gridless aperture, means aligned with said resonator means for projecting an electron beam having substantially longitudinally spaced concentrations in electron density therealong through said resonator field substantially centrally of said aperture, electron-focusing means located adjacent said electron projecting means for directing said beam toward a predetermined point, and conductive electron interceptor means mounted in the vicinity of said point in the path of said beam and having a portion forwardly of said aperture and out of said electromagnetic field for intercepting the centrally disposed electrons in said beam to prevent interaction of said centrally disposed electrons with said field.

ROBERT L. WATI-IEN. RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,506 Hahn June 27, 1944 2,064,469 Haeif Dec. 15, 1936 2,254,796 Doring Sept. 2, 1941 2,259,690 Hansen Oct. 21, 1941 2,280,026 Brown Apr. 14, 1942 2,284,829 Ludi June 2, 1942 2,295,315 Wolff Sept. 8, 1942 2,305,844 Clark Dec. 22, 1942 2,316,264 Litton Apr. 13, 1943 2,329,780 Zalesak Sept. 21, 1943 2,343,487 Steudel Mar. 7, 1944 2,351,757 Gray June 20, 1944 2,403,795 Hahn July 9, 1946 2,405,611 Samuel Aug. 13, 1946 2,406,370 Hansen et a1. Aug. 27, 1946 2,409,179 Anderson Oct. 15, 1946 2,409,644 Samuel Oct. 22, 1946 

